METHOD AND ARRANGEMENT FOR CONTROLLING THE OPERATION OF A HIGH-FREQUENCY POWER AMPLIFIER

Abstract: The invention relates to a method and an arrangement for controlling the operation of a high-frequency power amplifier. The arrangement comprises a high-frequency power amplifier (1) connected to a forward line (A) and a control means (2) and an attenuation means (3) connected to the input side thereof. A sampling means (4) and a detector (5) means are connected to a feedback line (B) between the output side and the input side of the high-frequency power amplifier. An amplifying means (7) is connected to the feedback line (B) on the input side of the detector means (5), the gain of which means is of the same order of magnitude as the attenuation of the attenuation means (3).

Description: Method and arrangement for controlling the operation of a high-frequency power amplifier The invention relates to a method and an ar- rangement for controlling the operation of a high-fre¬ quency power amplifier. The method comprises inputting a signal to be amplified to a high-frequency power am¬ plifier in a forward line, generating a sample signal from the forward line on the output side of the high- frequency power amplifier to a feedback line, control¬ ling the high-frequency power amplifier via the feedback line on the basis of the sample signal by a control means connected to the input side of the high-frequency power amplifier and bringing the high-frequency power amplifier to an OFF state controlled by a control sig¬ nal. The arrangement according to the invention comprises a high-frequency power amplifier connected to a forward line, a control means and an attenuation means connected to the input side of the high-frequency power amplifier and a sampling means and a detector means con¬ nected to a feedback line between the output side and input side of the high-frequency power amplifier. The forward line and the feedback line form a kind of a power control loop, by means of which the power of a transmitter is connectable to an antenna. The present solution relates especially to mul¬ tichannel radio transmitters and how to switch on the transmission power of a high-frequency power amplifier of a radio transmitter and particularly how to switch off the transmission power, i.e. how to bring it to an OFF state. One example of radio transmitters is a base station radio transmitter of a GSM mobile telephone network utilizing a TDMA system, the high-frequency power amplifier of which transmitter amplifies the sig- nals to be received from a modulator before these are inputted to an antenna. In GSM transmitters, for instance, specifica¬ tions place rigid restrictions also on the operation of the transmitter as well as on switching on or off the transmission power. When the transmission power is switched off at a GSM transmission, it should be pos¬ sible to reduce the transmission power during idle time slots between frames by at least 70 dB, in practice by 80 dB, which can be realized by decreased gain and by using RF switching means providing an attenuation of about 40 dB, in addition to the 40 dB obtained by the control of the amplifier. One problem with the previous solutions is that the dynamic range of detector means is only about 40 dB. In some methods and arrangements according to the prior art, the transmission power is switched off by using a switching means positioned in a power control loop on the input side of an amplifier, whereby the signal path breaks, however, and the detector output remains floating in a way. This generates a control sig¬ nal undefined in its details in a control means of the input side of the amplifier, which in turn causes pro¬ blems, i.e. practically a control error in a situation when the transmission power shall be switched on again. A control error may also cause a decrease in attenuation when the power is switched off. This restricts the per¬ mitted maximum gain between the detector and the control means as well, which maximum gain determines in turn the accuracy of the output power in an ON state. In another known embodiment, a switching means is positioned in an antenna line outside a power control loop, which requires, however, an amplifier and an RF switch with a higher power, which leads to bigger power losses. It is also known from the prior art to use a logarithmic RF range amplifier and detector to expand the dynamic range of the detector, but the component in question is an expensive hybrid component and thus not necessarily a suitable choice always. From European Patent Application 0 135 154 is known an apparatus for controlling transmission power, but no reference is made therein to bringing an ampli¬ fier to an OFF state. The objective of the apparatus disclosed in said publication is to minimize variations in loop gain caused by the non-linearity of the power amplifier. Said publication relates to controlling DC gain and by no means to controlling RF gain or RF atte¬ nuation, which is the case in the present invention. In the solution disclosed in said EP publication, the con¬ trol of a power control loop comes from inside the loop. The object of the present invention is to set forth a novel method and arrangement for controlling the operation of a high-frequency power amplifier, which avoid the problems associated with the known solutions. This object is achieved by means of the method according to the invention, which is characterized in that the high-frequency power amplifier is brought to the OFF state without breaking the signal path by atte- nuating the signal to be inputted to the input side of the high-frequency power amplifier by a desired attenu¬ ation and by amplifying the signal of the feedback line by a desired gain. The arrangement according to the invention is characterized in that an amplifying means is connected to the feedback line on the input side of the detector, the gain of which means is of the same order of magnitude as the attenuation of the attenuation means. The method and arrangement according to the in- vention are based on the idea that both attenuation and gain are supplied to the power control loop without breaking the signal path, due to which the detector means does not react to switching off the transmission power in a detrimental manner, which caused control error in the previous solutions. Several advantages are achieved by means of the solution according to the invention especially therein that the power control loop does not break, not even when the power is switched off, due to which a narrower frequency spectrum and a faster reaction to reswitching the gain are provided. In the solution of the invention, the properties of the high-frequency power amplifier are better than in the known solutions, both during gain and when the power is switched on or off. The new solution provides a smaller power loss than a solution the switching means of which is in an antenna line. The new solution also provides a more accurate output power than a solution the switching means of which is on the input side of the power amplifier. In the following, the invention will be de¬ scribed in more detail referring to the attached draw¬ ings, in which Figure 1 shows a block diagram of an arrange¬ ment according to the invention, Figure 2 shows an embodiment of the position of an amplifying means of a feedback line. The arrangement of Figure 1 comprises a power control loop constituted by a forward line A and a feed¬ back line B. The arrangement comprises a high-frequency power amplifier 1 connected to the forward line A, a control means 2 and an attenuation means 3 connected to the input side of the high-frequency power amplifier 1. The control means 2 may be realized by means of a volt¬ age-controlled attenuator (VCA), for instance, and the attenuation means 3 may in turn be realized for example by means of switches and resistances in such a way that either an attenuation of 40 dB or a very small attenu¬ ation is achieved by the attenuation means. Indication P(IN) represents the input side, to which a signal to be amplified comes from a modulator of a transmitter and indication P(OUT) represents an antenna line starting from the output side of the amplifier. In addition, the arrangement comprises a sampling means 4 and a detector means 5 connected to the feedback line B between the output side and the input side of the amplifier. The sampling means 4 may preferably be constituted by a directional coupler, such as a microstrip directional coupler, by which from an output signal of the amplifier is generated a sample signal 6 proportional to the strength of the output signal. The sample signal 6 is detected by the detector means 5, which may be consti¬ tuted by a rectifier implemented by means of diodes, for instance. To the feedback line B on the input side of the detector 5 is connected an amplifying means 7, the gain of which is of the same order of magnitude, preferably very exactly the same, as the attenuation of the attenu¬ ation means 3 on the input side of the high-frequency power amplifier 1. The preferred embodiment of Figure 1 shows that the attenuation means 3 not breaking the signal path is connected between the control means 2 and the high-frequency power amplifier 1 and that the ampli¬ fying means 7 of the feedback line B is connected be¬ tween the directional coupler acting as the sampling means 4 and the detector means 5. Referring further to Figure 1, the arrangement also comprises a control unit 8, a summer 9 and a low-pass filter 10. The attenuation means 3 not breaking the signal path may be connected alternatively in front of the con- trol means 2, in which case the control means 2 and the attenuation means 3 would thus be in opposite order in Figure 1. The method for controlling the operation of a high-frequency power amplifier comprises inputting a signal to be amplified to a high-frequency power ampli¬ fier 1 in a forward line A, generating a sample signal from the forward line A on the output side of the high- frequency power amplifier 1 to a feedback line B by means of a sampling means 4. The method further com- prises detecting the sample signal by a detector means 5, summing the detected sample signal to a reference signal 11 to be obtained from a control unit 8, low-pass filtering the summation signal 12 by a low-pass filter 10 and gain, if necessary. The method also comprises controlling the gain of the high-frequency power ampli¬ fier 1 on the basis of the detected, summed and filtered sample signal by a control means 2 connected to the input side of the high-frequency power amplifier. When the power is switched off, the method also comprises bringing the high-frequency power amplifier 1 to an OFF state controlled by control signals 13 and 14, which control signals 13 and 14 are generated in the control unit 8. The high-frequency power amplifier is brought to the OFF state, without breaking the signal path, by attenuating the signal to be inputted to the input side of the high-frequency power amplifier 1 by an attenua¬ tion means 3 with a desired attenuation and by ampli¬ fying the signal of the feedback line B with a desired gain and preferably expressly as much as the signal of the input side was attenuated. In this case, the attenu¬ ation to which the forward line A of the input side of the high-frequency power amplifier 1 shall be exposed is substantially equal to the gain to which the feedback line shall be exposed, thanks to which the detector means 5 omits to react to switching off the power better and better and is thus capable of avoiding control errors. The voltage-controlled control means 2 performs an attenuation of 40 dB and the attenuation means 3 performs another attenuation of still 40 dB, thanks to which the signal to be connected is attenuated by 80 dB, which is enough. In order not to exceed the dynamic range of the detector 5, a signal passing simultaneously to the detector 5 in the feedback line is amplified with 40 dB by an amplifying means 7. As the amplifying means 7 of the feedback line is used a switched gain amplifier with a gain of 40 dB, for instance. The amplifying means 7 is active only in an OFF state of power switching when the power of the high-frequency amplifier itself is switched off. Correspondingly, as the attenuation means 3 is used a switched attenuator with an attenuation of 40 dB, for instance, which attenuator is active only in an OFF state when the power of the high-frequency power amplifier itself is switched off. In a preferred embodi- ment, the attenuation of the forward line A and the gain of the feedback line B are switched on by the common control unit 8 according to Figure 1, and expressly by the same control unit 8 by which the reference signal 11 is inputted to the summer 12, making a solution pos- sible which is structurally the simplest and the easiest to implement. The control unit 8 constitutes an external control means 8 with respect to the loop, by which means RF attenuation and RF gain are controlled. In a preferred embodiment, separate detector means are used for detecting separate power ranges. These separate detector means have sensitivities devia¬ ting from each other, the first detector means being used for detecting an OFF state and the second detector means being used for detecting an ON state. The sensi- tivities are selected in such a way that the detector means which is active in an OFF state, i.e. when power is switched off, is more sensitive. Figure 2 shows an embodiment of the position of the amplifying means 7 of the feedback line. In Fig- ure 2, the input side IN is connected to the sampling means 4 of Figure 1 and the output side OUT is connected to the detector 5 of Figure 1. In the embodiment of Fig¬ ure 2, the arrangement comprises a first switching means 51 connected in series with the amplifying means 7 of the feedback line, and the arrangement comprises further a second and a third switching means 52 and 53 and a conductor means 54 between them. The second and the third switching means 52 and 53 can be connected in series either with the conductor means 54 or with the first switching means 51 and the amplifying means. The switching means 51 to 53 are arranged under common con¬ trol, the upper position of Figure 2 showing a normal situation with no gain supplied to the feedback line. In a situation with the switches 51 to 53 in the lower position, a gain of about 40 dB is supplied to the feed¬ back line, i.e. as much as the forward signal is attenu¬ ated by the attenuation means 3 of Figure 1. As far as choice of components is concerned, the solution of Fig¬ ure 2 is a preferred embodiment, since switching means at fair cost are used therein. The typical attenuation capacity of the switching means of SPDT type shown in Figure 2 is about 30 dB at GSM frequencies. In Figure 2, with the switch 51 in open posi¬ tion, i.e. in the upper position, the amplifier is con- nected to a terminal 55, which may be implemented by means of a resistance, for instance. The advantage is then achieved that the input of the amplifier 7 does not remain open when the switch 51 is open. Accordingly, the amplifying means 7 is on its input side connectable to the input IN via the switches 51 and 52 when they are in the lower position, or alternatively, the amplifying means 7 is connectable via the switch 51 to the ter¬ minal, in this case to the resistance 55, when the switches 51 and 52 are in the upper position. The solution according to Figure 2 is presented only as an example, i.e. as one preferred embodiment, and it is clear that the solution of Figure 2 also has several alternative embodiments, such as the one in which the two signal paths between the input and output shown in Figure 2 may comprise a separate directional coupler and/or a detector means. In one preferred embodiment, different amplifi¬ cation values are provided by changing the sample signal 6 to be taken from the output side of the high-frequency power amplifier 1 and coming to the amplifying means 7. This is preferably made possible by means of at least two separate directional couplers contained in the input side of the amplifying means 7, or by a corresponding means, the output signals of which deviate from each other. Though the invention has been described above with reference to the examples according to the attached drawings, it is clear that the invention is not re¬ stricted to them, but it can be modified in many ways within the scope of the inventive idea set forth in the attached claims.

Claims: Claims: 1. A method for controlling the operation of a high-frequency power amplifier, the method comprising - inputting a signal to be amplified to a high-frequency power amplifier (1) in a forward line (A), - generating a sample signal (6) from the forward line (A) on the output side of the high-frequency power am¬ plifier (1) to a feedback line (B), - controlling the high-frequency power amplifier (1) via the feedback line (B) on the basis of the sample signal by a control means (2) connected to the input side of the high-frequency power amplifier (1), and - bringing the high-frequency power amplifier (1) to an OFF state controlled by a control signal (13, 14), c h a r a c t e r i z e d in that the high-frequency power amplifier (1) is brought to the OFF state without breaking the signal path by attenuating the signal to be inputted to the input side of the high-frequency power amplifier (1) by a desired attenuation and by am¬ plifying the signal of the feedback line (B) by a desired gain. 2. A method according to claim 1, c h a r ¬ a c t e r i z e d in that the attenuation to which the forward line (A) on the input side of the high-frequency power amplifier (1) is exposed is essentially equal to the gain to which the feedback line (B) is exposed. 3. A method according to claim 1 or 2, c h a r a c t e r i z e d in that the attenuation of the forward line (A) and the gain of the feedback line (B) are connected by a common control unit (8) . 4. A method according to claim 1, 2 or 3, c h a r a c t e r i z e d in that different amplifica¬ tion values are provided by changing the sample signal (6) to be taken from the output side of the high-fre- quency power amplifier (1) and coming to the amplifying means (7) . 5. A method according to claim 4, c h a r ¬ a c t e r i z e d in that the provision of the differ- ent amplification values is made possible by at least two separate directional couplers or the like contained in the input side of the amplifying means (7). 6. An arrangement for controlling a high-fre¬ quency power amplifier, comprising a high-frequency power amplifier (1) connected to a forward line (A), a control means (2) and an attenuation means (3) connected to the input side of the high-frequency power amplifier and a sampling means (4) and a detector (5) means con¬ nected to a feedback line (B) between the output side and the input side of the high-frequency power amplifier (1), c h a r a c t e r i z e d in that an amplifying means (7) is connected to the feedback line (B) on the input side of the detector means (5), the gain of which means is of the same order of magnitude as the attenua- tion of the attenuation means (3) . 7. An arrangement according to claim 6, c h a r a c t e r i z e d in that the attenuation means (3) not breaking the signal path is connected between the control means (2) and the high-frequency power am- plifier (1) or in front of the control means (2) and that the amplifying means (7) of the feedback line (B) is connected between the directional coupler acting as the sampling means (4) and the detector means (5). 8. An arrangement according to claim 6 or 7, c h a r a c t e r i z e d in that the arrangement com¬ prises a first switching means (51) connected in series with the amplifying means (7) of the feedback line (B), and the arrangement comprises further a second and a third switching means (52, 53) and a conductor means (54) between them and that the second and the third switching means (52, 53) can be connected in series either with the conductor means (54) or with the first switching means (51) and the amplifying means (7). 9. An arrangement according to claim 8, c h a r a c t e r i z e d in that, with the input side of the amplifying means (7) switched off by the first switching means (51 ), the input of the amplifying means (7) is connected to a terminal (55), preferably to a resistance. 10. An arrangement according to claim 6, 7 or 8, c h a r a c t e r i z e d in that separate detector means are used for detecting separate power ranges.

Inventors: DEKKER ANDRE, DEKKER, ANDRE
Applicants: DEKKER ANDRE, NOKIA TELECOMMUNICATIONS OY, DEKKER, ANDRE
Application year: 1994
Main classification: H03G3
IPC codes: H03F1, H03F3, H03G3, H04B1